/*
 * Copyright 2000-2016 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.intellij.util.concurrency;

import com.intellij.openapi.diagnostic.Logger;

import java.util.concurrent.DelayQueue;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * This class implements the global delayed queue which is used by
 * {@link AppScheduledExecutorService}.
 * It starts the background thread which polls the queue for tasks ready to run and sends them to the appropriate executor.
 * The {@link #shutdown()} must be called before disposal.
 */
class AppDelayQueue extends DelayQueue<SchedulingWrapper.MyScheduledFutureTask> {
    private static final Logger LOG = Logger.getInstance("#com.intellij.util.concurrency.AppDelayQueue");
    private final Thread scheduledToPooledTransferer;
    private final AtomicBoolean shutdown = new AtomicBoolean();

    AppDelayQueue() {
    /* this thread takes the ready-to-execute scheduled tasks off the queue and passes them for immediate execution to {@link SchedulingWrapper#backendExecutorService} */
        scheduledToPooledTransferer = new Thread(new Runnable() {
            @Override
            public void run() {
                while (!shutdown.get()) {
                    try {
                        final SchedulingWrapper.MyScheduledFutureTask task = take();
                        if (LOG.isTraceEnabled()) {
                            LOG.trace("Took " + task.toString());
                        }
                        if (!task.isDone()) {  // can be cancelled already
                            task.getBackendExecutorService().execute(task);
                        }
                    } catch (InterruptedException e) {
                        if (!shutdown.get()) {
                            LOG.error(e);
                        }
                    }
                }
                LOG.debug("scheduledToPooledTransferer Stopped");
            }
        }, "Periodic tasks thread");
        scheduledToPooledTransferer.start();
    }

    void shutdown() {
        if (shutdown.getAndSet(true)) {
            throw new IllegalStateException("Already shutdown");
        }
        scheduledToPooledTransferer.interrupt();

        try {
            scheduledToPooledTransferer.join();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}
